The invention relates to double-acting forging hammers and, more particularly, to forging hammers actuated by pressurized gas and/or hydraulic fluid.
In its most basic form, a forging hammer consists of a frame which supports a lower die and a cylinder oriented vertically above the lower die, a piston slidably mounted within the cylinder and having a piston rod extending downwardly therefrom, a relatively large and massive hammer connected to the piston rod and mounting an upper die in registry with the lower die, and means for introducing a pressurized gas or fluid into the cylinder below the piston to raise the piston and hammer. Early forms of such forging hammers utilized steam as the pressurized gas which was introduced into the cylinder to raise the hammer. The downward force which lowered the hammer in the forging stroke consisted solely of the force resulting from the pull of gravity on the mass of the hammer, piston and piston rod.
Later embodiments of forging hammers included means for introducing steam into the cylinder above the piston to urge the piston downwardly during the forging stroke thereby accelerating the rate at which the hammer fell during the forging stroke. The force generated could exceed the force generated by a similarly sized hammer which was urged downwardly merely by the force of gravity.
However, steam-operated forging hammers possessed many disadvantages. Generating steam required the use of boilers which had to be tended by firemen and had relatively high maintenance and safety-related costs, all adding to the expense of operation. Furthermore, the steam powered hammers were relatively inefficient in that the steam evacuated from the cylinder during a forging or return stroke was typically vented to the atmosphere, resulting in a loss of energy in the form of heat from the overall system. Proper operation of such hammers required highly skilled and trained operators who had learned how to control the steam or air valves to achieve just the right impact force.
Subsequent forging hammers utilized pneumatic or hydraulic systems in which a compressible gas or a hydraulic fluid was forced into the cylinder by pumps in place of steam. A disadvantage of pneumatic systems, such as that disclosed in Weyer U.S. Pat. No. 3,464,315, is that at least a portion of the air is exhausted to the atmosphere at the end of the forging and/or return strokes, requiring the pumps to generate additional compressed air and decreasing the overall operating efficiency of the system. Another disadvantage of such systems is that relatively high pressure air must be generated, requiring heavy duty compressors which add to the cost of the system.
Hydraulic systems, such as that disclosed in the Hassel U.S. Pat. No. 3,727,519, were typically closed systems in which hydraulic fluid would be stored in a reservoir and supplied to the cylinder by pumps to move the piston. At the same time, the hydraulic fluid within cylinder which was not acting on the piston therein would be evacuated from the cylinder and would flow back to the reservoir. A disadvantage of such systems is that they required complex components and extensive piping, which add to the overall cost of the system.
Accordingly, there is a need for a double-acting forging hammer which utilizes pneumatic and/or hydraulic hammer driving systems, yet does not have the energy losses associated with pneumatic systems or the complex and sophisticated components of hydraulic systems. Furthermore, there is a need for a pneumatic and/or hydraulic hammer driving system which can be retrofitted easily to existing forging hammers.